Unequivoca l Proof 1952 Worked with Bacteriophage Attaches to bacteria Genetic Material in cell Cell treats it as its own More Virus particles synthesized Whether protein has entered or DNA ID: 912213
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Slide1
Slide2Slide3Slide4Slide5Slide6Slide7Slide8Slide9Hershey and Chase Experiment
Unequivoca
l Proof
1952
Worked with Bacteriophage
Attaches to bacteria Genetic Material in cell Cell treats it as its own More Virus particles synthesized
Whether protein has entered or DNA
Slide10Bacteriophage
A bacteriophage is a
type of virus
that infects
bacteria
.
In fact, the word "bacteriophage" literally means "
bacteria eater
," because bacteriophages destroy their host
cells
.
All bacteriophages are composed of a
nucleic acid molecule that is surrounded by a protein structure.
Slide11Structure
Slide12Slide13Slide14Slide15Slide16Hershey and Chase conducted an experiment to discover whether it was protein or DNA that acted as the genetic material that entered the bacteria
Experiment:
The experiment began with the culturing of viruses in two types of medium.
One set of viruses (
A) was cultured in a medium of radioactive phosphorus whereas
another set
(B) was cultured in a medium of radioactive sulfur
.
Slide17observations
They observed that the first set of viruses (A) consisted of
radioactive DNA
but not radioactive
proteins
.
This is because DNA is a phosphorus-based compound while protein is not. The latter set of
viruses (B) consisted of radioactive protein
but not radioactive DNA.
The
host for infection was E.coli bacteria
. The viruses were allowed to infect bacteria by removing the viral coats through a number of blending and centrifugation
Slide18Slide19Properties of Genetic Material
In some viruses RNA – Genetic Material
Examples- TMV,QB bacteriophage
What criteria a molecule must fulfill in order to act as a genetic material
?
Slide20Criteria
Replication
Stability
Scope for Mutation
Mendelian Characters
Slide21Contd.
DNA and RNA both direct their duplications
Proteins Cant direct their duplication
Stability From Griffth Exptt. Its evident DNA was more stable.
Also 2’OH group in RNA makes it easily degradable.
RNA is unstable so mutates at a faster rate
Slide22Contd.
Viruses have RNA as genetic material and can mutate and evolve faster!!!!
Protein synthesis evolved around RNA.
DNA is stable for storing genetic information
But to transfer information RNA is required.
RNA first genetic material, can act as a catalyst, hence unstable!
Slide23Slide24While DNA contains
deoxyribose
, RNA contains
ribose
, characterised by the presence of the 2'-hydroxyl group on the pentose ring.
This hydroxyl group make RNA less stable than DNA because it is more susceptible to hydrolysis.
RNA contains the
unmethylated
form of the base thymine called
uracil
(U) which gives the nucleotide uridine
Slide25Chemical structure of RNA: nucleotides containing a ribose sugar (carbons numbered 1' through 5') with a base attached to the 1' position